总结：MulitpartResolver用于处理上传请求，springmvc没有默认的配置如果需要使用需要手动配置。
MulitpartResolver中总共有三个方法（判断是不是上传请求、将request包装成MultipartHttpServletRequest、清除上传过程中产生的临时资源），两个实现类（一个Servlet 3.0，一个基于commons-upload）。
一、MulitpartResolver接口中三个方法：
public interface MultipartResolver {
/**
* 判定是不是上传请求"multipart/form-data"
*/
boolean isMultipart(HttpServletRequest request);
/**
* 将http请求解析成multipart文件及参数
*/
MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException;
/**
* 清除上传中的临时文件
*/
void cleanupMultipart(MultipartHttpServletRequest request);
}
二、两个默认的实现类
1）基于Servlet 3.0的StandardServletMultipartResolver
public class StandardServletMultipartResolver implements MultipartResolver {
private boolean resolveLazily = false;//默认false，立即
public void setResolveLazily(boolean resolveLazily) {
this.resolveLazily = resolveLazily;
}
@Override
public boolean isMultipart(HttpServletRequest request) {
if (!"post".equals(request.getMethod().toLowerCase())) {
return false;
}
String contentType = request.getContentType();
return (contentType != null && contentType.toLowerCase().startsWith("multipart/"));
}
@Override
public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
//StandardMultipartHttpServletRequest的实现后面会介绍
return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
}
@Override
public void cleanupMultipart(MultipartHttpServletRequest request) {
try {
for (Part part : request.getParts()) {
if (request.getFile(part.getName()) != null) {
part.delete();
}
}
}
catch (Exception ex) {
LogFactory.getLog(getClass()).warn("Failed to perform cleanup of multipart items", ex);
}
}
}
2）基于common-upload组件
public class CommonsMultipartResolver extends CommonsFileUploadSupport
implements MultipartResolver, ServletContextAware {
private boolean resolveLazily = false;
public CommonsMultipartResolver() {
super();
}
public CommonsMultipartResolver(ServletContext servletContext) {
this();
setServletContext(servletContext);
}
public void setResolveLazily(boolean resolveLazily) {
this.resolveLazily = resolveLazily;
}
@Override
protected FileUpload newFileUpload(FileItemFactory fileItemFactory) {
return new ServletFileUpload(fileItemFactory);
}
@Override
public void setServletContext(ServletContext servletContext) {
if (!isUploadTempDirSpecified()) {
getFileItemFactory().setRepository(WebUtils.getTempDir(servletContext));
}
}
@Override
public boolean isMultipart(HttpServletRequest request) {
return (request != null && ServletFileUpload.isMultipartContent(request));
}
@Override
public MultipartHttpServletRequest resolveMultipart(final HttpServletRequest request) throws MultipartException {
Assert.notNull(request, "Request must not be null");
if (this.resolveLazily) {
return new DefaultMultipartHttpServletRequest(request) {
@Override
protected void initializeMultipart() {
MultipartParsingResult parsingResult = parseRequest(request);
setMultipartFiles(parsingResult.getMultipartFiles());
setMultipartParameters(parsingResult.getMultipartParameters());
setMultipartParameterContentTypes(parsingResult.getMultipartParameterContentTypes());
}
};
}
else {
MultipartParsingResult parsingResult = parseRequest(request);
return new DefaultMultipartHttpServletRequest(request, parsingResult.getMultipartFiles(),
parsingResult.getMultipartParameters(), parsingResult.getMultipartParameterContentTypes());
}
}
protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException {
String encoding = determineEncoding(request);
FileUpload fileUpload = prepareFileUpload(encoding);
try {
List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
return parseFileItems(fileItems, encoding);
}
catch (FileUploadBase.SizeLimitExceededException ex) {
throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
}
catch (FileUploadBase.FileSizeLimitExceededException ex) {
throw new MaxUploadSizeExceededException(fileUpload.getFileSizeMax(), ex);
}
catch (FileUploadException ex) {
throw new MultipartException("Failed to parse multipart servlet request", ex);
}
}
protected String determineEncoding(HttpServletRequest request) {
String encoding = request.getCharacterEncoding();
if (encoding == null) {
encoding = getDefaultEncoding();
}
return encoding;
}
@Override
public void cleanupMultipart(MultipartHttpServletRequest request) {
if (request != null) {
try {
cleanupFileItems(request.getMultiFileMap());
}
catch (Throwable ex) {
logger.warn("Failed to perform multipart cleanup for servlet request", ex);
}
}
}
}
